Method of treating sulfur bearing mineral values with molten sulfur to concentrate mineral sulfides



United States Patent "lice METHOD OF TREATING SULFUR BEARING MINERAL VALUES WITH MOLTEN SUL- FiUgl STO CONCENTRATE MMERAL SUL- F E John K. Kaufman, Irvington, and Tulrin K. Roy, Elizabeth, N. J., assignors to Chemical Construction Corporation, New York, N. Y., a corporation of Delaware N Drawing. Application October 22, 1953 Serial No. 387,801

7 Claims. (Ci. 75--2) This invention relates to the concentration of mineral values. More particularly, it relates to a method of treating a wide variety of sulfur-bearing materials containing mineral values such, for instance, as pyrrhotitic mineral sulfide ores and concentrates, native sulfur-bearing ores, and mixtures of sulfur-bearing and sulfide bearing materials to recover a concentrate of mineral values.

Various processes are known for concentrating mineral values. One of the most important and most widely used of these is the froth flotation process. Beneficiation of mineral sulfide ores by froth flotation is a standardized procedure carried out in acid, neutral or alkaline circuits in the presence of a promoter and usually a frothing agent. There are ores, however, such as various pyrrhotitic mineral sulfide ores, which are not directly or easily amenable to conventional flotation processes.

More recently, there has been suggested a treatment for native sulfur-bearing ores which comprises heating an aqueous slurry of ore above the melting point of sulfur. Resultant liquid sulfur agglomerates are solidified by cooling, and slurry subjected to conventional froth flotation. In this manner both an elemental sulfur product and a mineral values product are obtained. Much of the original mineral values content, however, becomes associated with the elemental sulfur during agglomeration. There has also been suggested a wet oxidation treatment of pyrrhotitic sulfide materials under elevated temperatures and pressures in which the sulfide content is oxidized to elemental sulfur which in turn is similarly melted, agglomerated and separated, leaving a concentrate of mineral sulfides. This sulfers from similar disadvantages.

It is the object of the present invention to overcome these diificulties by a relatively simple and straightforward process for treating any of such materials to obtain a concentrate of mineral sulfides. This object has been accomplished in a surprisingly successful manner. In general, the present process comprises heating a water or aqueous sulfuric acid slurry of such material containing elemental sulfur to a temperature above the melting point of sulfur to melt the sulfur particles. Resultant liquid elemental sulfur wets the surfaces of the mineral value particles causing them to associate with the liquid sulfur phase. The slurry of agglomerated liquid sulfur is then cooled to solidify the agglomerates. Cooled slurry is screened or otherwise treated to separate the sulfur pellets. These are reslurried in the water and, in the presence of a suitable surface-modifying agent for the mineral values, heated to reagglomerate the sulfur away from the metal values. Cooling and screening of the cooled reagglomerated slurry yields a high concentration of mineral values.

Although the above general statement of the process of this invention has been simply express there are conditions which must be observed to obtain optimum results.

The nature of the sulfur source or the nature of the 2,838,391 Patented June 10, 1958 original procedure for releasing sulfur to be used for collecting metal values is irrelevant to the process of this invention; Such procedure will usually comprise treating some sulfur-bearing material such "as, for instance, a native sulfur-bearing ore or a pyrrhotitic mineral sulfide ore or concentrate. The latter may be' naturallyoccurring minerals or may be obtained as a result of partially oxidizing some pyritic sulfides in a roasting or kindred process. The pyrrhotitic sulfides will usually be iron sulfides and may and usually will have associated therewith various non-metal sulfides and/or precious metals. As used herein, the term pyrrhotitic ore or concentrate is meant to include any material in which an appreciable part of the sulfur content is in a form similar to that in which it is combined in pyrrhotite. Besides pyrrhotite, per se, other such materials may include digenite, marcasite, arsenopyrite, tetrahedrite, bornite, chalcopyrite, sphalerite, enargenite, 'millerite and the like.

While oxidation of pyrrhotitic mineral sulfide materials to obtain a starting material for the process of this invention forms no part of the invention, it may very readily and usually will be carried out as a step in some commercial operation for other purposes. Accordingly, reference is made in the discussion of the invention, where necessary, to properly treat this situation.

Prior to treatment by the present invention, the starting material is preferably finely pulverized. The first step in the process, therefore, is crushing and/or grinding. While the size of the material may vary widely, it is preferably of the order of from about minus 35 to about plus 325 mesh U. S. standard screen. This is particularly important when elemental sulfur is obtained by oxidation of a pyrrhotitic mineral sulfide ore or concentrate, since reaction velocity and degree ofsulfur extraction appear to be best when treating a slurry having particles within this size range. When treating a native sulfur-bearing ore, pulverizing to this extent disintegrates a major portion of the native sulfur, leaving it in condition for easy agglomeration on subsequent heating. Material received from preliminary concentrating processes may already be of the preferred range. Material not already of the preferred size is preferably first reduced to about 35 mesh or finer.

Pulverized material is then slurried. This will generally be in water. However, when oxidation forms a part of the operation, oxidized slurry will be acid because of sulfate formation during oxidation. The hydrogen ion concentration of the slurry should be kept below about 3.3 to 3.5 but preferably the free acid content should not exceed about pH 1. 'Dissolution of iron will I normally maintain the pH constant at about 2. If not,

some form of neutralization or limitation on the amount: of material treated in any. one cycle may be necessary.

At higher pH values, iron content of the starting material is likely to be converted to hydrated iron oxide with resultant gel formation, rendering subsequent screening difiicult. At higher acid concentrations, basic iron sulfates form. I

Pulp density of. the slurry may range 'as high .aslcan' be agitated and pumped. A most satisfactory range,

however, is from about 35% to about 50% solids. Higher densities excessively increase agitating and pumping requirements. At some stage heating the slurry of elemental sulfur bearing material to a temperature above the melting point of the sulfur in the slurry is necessary. Formation of are obtained in a temperature range of from about 260290 F. At higher temperatures, viscosity of the 3. liquid. sulfur is too high. Moreover, while in general the size of. sulfur droplets increases with higher temperatures, the gain at temperatures above 290 F. is not appreciable.

When. oxidation: of a pyrrhotitic mineral. sulfide material forms the source of elemental sulfur, oxidation may be conducted. within the temperature range noted above for agglomeration. Alternatively, it may be conducted in whole or in part at a temperature below the melting point of sulfur. In the latter case, the temperature will subsequently be raised to above the melting point of sulfur to melt and agglomerate the elemental sulfur as above described. In either event, the material is subjected to a temperature above the sulfur melting point for sufficient time to effect maximum metal values pickup. When oxidizing above the melting point of sulfur mineral value particles become associated with the liquid sulfur and are thus protected from oxidation.

When treating sulfur rock containing sulfides, much of the release of the sulfur must occur above the melting point. The period of molten sulfur agglomeration should be extended as long as necessary to obtain maximum sulfide pickup. The pressure at which agglomeration is conducted is the pressure generated by the temperature. When jointly conducting oxidation and agglomeration of a pyrrhotitic mineral sulfide material, total pressure will include the partial pressure of the oxygen-bearing oxidizing gas. For purposes of such oxidation, the oxidizing gas may be oxygen, oxygen-enriched air or air. The most satisfactory results as regards velocity of reaction and extent of extraction of sulfur are obtained with a partial pressure of oxygen of about 25 p. s. i. to about 100 p. s. i.

Liquid sulfur has the ability to wet the surface of small particles. Advantage of this characteristic is taken in the process of this invention to concentrate mineral sulfides and/r precious metals contained in the starting material. The time required to form liquid droplets of elemental sulfur and obtain optimum association therewith of mineral sulfides and precious metals is influenced by agitation. With agitation, agglomeration is conducted for suificient time to associate a maximum of the mineral sulfides and/or precious metals with sulfur droplets of a size which may be easily recovered on cooling. In general, it will require about -15 minutes to complete treatment. It may, however, in some instances, be completed in a shorter period, while in other cases it may even require a longer period.

After agglomeration is complete, the agglomerated sulfur slurry is cooled to below the melting point of sulfur to solidify the liquid agglomerates of sulfur. Cooling may be accomplished indirectly, by direct water injection, by flashing off. steam or in any other suitable manner, preferably without agitation. The temperature to which the agglomerated sulfur slurry is reduced is not particularly critical, it being only necessary to reduce the temperature below the melting point of sulfur in the slurry. Cooled slurry is then treated to recover the sulfur pellets as, for instance, by being passed over a screen having openings of sufiicient size to retain the sulfur pellets While passing the solution and undissolved residue.

A novel feature of this invention is the treatment of the elemental sulfur pellets,sregardless of the method of sulfur liberation, agglomeration and collection to recover mineral values associated therewith. In general, this is accomplished by reslurrying the pellets and heating, in the presence of a surface modifying agent for the mineral values, to reagglomerate the sulfur. Reagglomerated slurry is then cooled and subjected to separation to collect a concentration of mineral values.

The conditions under which reagglomeration is conducted are, in general, similar to the conditions for acid agglomeration. Pulp density of the water slurry of elemental sulfur pellets again is preferably in the range of about to solids. As in acid agglomeration, the

4 slurry is heated in a reaction vessel at temperatures above the sulfur melting point, preferably between 260-290 F.

Reagglomeration differs from acid agglomeration, however, in that it is conducted in the presence of an agent designed to modify the surfaces of the mineral values particles. in this manner, the Wetting action of the liquid sulfur on the metal and/ or metal sulfide particles is overcome, thereby releasing substantially all the particles from their association with the sulfur.

Numerous surface modifying agents are known which are suitable and may be employed in the practice of this invention. One of the simplest for use herein are the alkaline-earth metal oxides or hydroxides, i. e., lime and the like. In general, any agent suitable for use as a sulfide depressant in froth flotation may be used. These include not only lime but such materials as the alkali-metal cyanides and silicates, and such organic agents as tannin, quebracho, nigrosin, dextrin, the lignin sulfonates and the like.

Reagglomeration is conducted with agitation. Intensity and extent of agitation and temperature influence, to some extent, the time required for maximum reagglomeration of sulfur away from the mineral particles. These factors also influence the size of liquid sulfur droplets. In general, maximum dissociation of mineral sulfide particles and formation of sulfur droplets, which on cooling may be easily separated, will occur in a few minutes, but may require as much as 15 or more minutes. The slurry is then cooled in a manner and to an extent described with respect to acid agglomeration. Cooled slurry is subjected to screening or the like to separate and collect a valuable concentrate of mineral sulfides and precious metals.

The following examples further illustrate the invention. All parts are by weight unless otherwise noted.

A sample of native sulfur rock assaying 34.1% total sulfur, 27.3 free sulfur, 1.4% $0,, 7.8% iron and 41% SiO was ground to pass a 28 mesh U. S. standard screen and divided into a number of portions for testing.

Example 1 250 parts of ore are slurried in 750 parts of water to about a 25% solids slurry, heated with agitation at about 265270 F. for about one minute, then cooled to about 180-190 F. by addition of cold water, passed over a 28 mesh screen and about 0.6 parts of screen oversize removed as a sulfur product assaying about 98% sulfur. Screen undersize is subjected to froth flotation at about 170180 F. for about 3 minutes at about 20% solids using 0.01 lb./ton of pine oil and 0.02 lb./ton of sodium dicresyldithiodiphosphate to obtain a concentrate containing about of the original sulfur at 78% free sulfur content and containing about 55% of the sulfide sulfur.

Example 2 300 parts of sulfur-sulfide flotation concentrate produced in Example I is repulped with water containing 2 parts of lime to about 30% solids, heated to about 275 F. and stirred without additional air in a pressure vessel for about 10 minutes, cooled to about 180 F. and passed over a 60 mesh screen. About 90% of the original sulfur at about 93% sulfur content is recovered from the screen oversize. A concentrate containing 54% pyrite is recovered by dewatering the screen undersize.

Example 3 Example 1 is repeated but the agglomeration period for the original slurry is increased to 10 minutes at about 275 F. It is then cooled and passed over a 60 mesh screen. Screen oversize containing nearly 80% of the sulfide sulfur, is repulped to about 30% solids in water containing 2 parts of lime and stirred for about 10 minutes at 275 F., cooled by flashing off steam to about F., diluted to about 20% solids and given a rougher flotation for about 3 minutes with 0.01 lb./ton of pine oil and 0.3 lb./ ton of fuel oil. The rougher concentrate assays about 95% of the original sulfur at about 93% sulfur. The tailings contain about 0.4% of the sulfur and about 80% of the original sulfide content.

Example 4 A pyrrhotitic nickel sulfide concentrate is found to assay 3.5% nickel, 4.3% copper, 49.3% iron and 29.7% sulfur. 400 parts are ground to pass 28 mesh, slurried with water to about 30% solids and heated with stirring at 230 F. under 200 p. s. i. g. oxygen pressure for about two hours, then for about five minutes at 260 F., cooled to below 190 F. and passed over .a 30 mesh screen. Oversize is reslurried at about 25% solids in water containing suflicient lime to produce a pH of about 9.0 and heated for about minutes at 275 F., cooled by flashing off steam and separated at about 80 mesh. Undersize is found to contain substantially all of the unaltered nickel, copper and iron sulfides. The plus 80 mesh fraction is substantially sulfur of about 97% purity.

1 The following examples illustrate the use of other surface modifying agents.

Example 5 A low grade sulfur ore assaying 27% free sulfur and 11% sulfide sulfur is treated as in Example 3. The screen oversize comprises 65% sulfur representing 92% recovery and 18.7% sulfides representing 65% overall recovery. 300 parts of this oversize product is slurried to 30% solids with water containing 4 parts of sodium carbonate, heated to 265 F. for two minutes, cooled and subjected to flotation. The tailing contains about 5% sulfur and about 55% pyrite representing a 60% overall sulfide recovery.

Example 6 The procedure of Example 5 is repeated except that 300 parts of the screen oversize is slurried to 30% solids in water containing 2 parts of sodium hydroxide as the surface modifying agent. Reagglomerated slurry is floated and a tailing obtained containing about 3.2% sulfur and 53% pyrite representing .a 55% overall sulfide recovery.

Example 7 Example 5 is repeated except that 300 parts of screen oversize is slurried to 30% solids in water containing 2 parts of sodium silicate as a surface modifying agent. Flotation tailing contains 4.0% sulfur and 52% pyrite representing a 54% overall sulfide recovery.

As noted above, there is incidentally produced in the practice of this invention an elemental sulfur product. While the process of this invention is concerned with concentrating mineral values contained in various sulfurbearing materials, copending application Serial No. 387,802 filed of even date by the same inventors discloses a modification of this process for recovering sulfur from such materials as high purity elemental sulfur.

We claim:

1. A method of treating a mixture comprising sulfur in association with metal values to obtain a concentrate of metal values in processes wherein an aqueous slurry of said mixture is heated to an elevated temperature above the melting point of sulfur to agglomerate the sulfur and said slurry is cooled to solidify the sulfur as pellets, which comprises: subjecting said slurry to said elevated temperature under conditions of time and agitation to form liquid sulfur droplets having therewith an optimum association of said metal values; cooling treated slurry and separating a single solid phase in the form of pellets comprising sulfur and metal values; dispersing said pellets in an aqueous medium to form a slurry; furnishing in said slurry a material which is capable of depressing sulfide minerals in the flotation of oxidized minerals; heating said slurry to a temperature above the melting point of sulfur therein; agitating said slurry and maintaining said temperature for at least suflicient time to separate sulfur from the metal values associated therewith; cooling said treated slurry to obtain sulfur and metal values as separate solid phases; and treating said cooled slurry to separate and collect a concentrate of metal values.

2. A method according to claim 1 in which the mixture of elemental sulfur and metal values is an oxidized pyrrhotitic mineral sulfide.

3. A method according to claim 1 in which the mixture of elemental sulfur and metal values is a native sulfurbearing ore.

4. A process according to claim 1 in which the surface modifying agent is selected from the group consisting of alkali metal oxides and hydroxides.

5. A process according to claim 1 in which the surface modifying agent is lime.

6. A' process according to claim 1 in which the metal values include mineral sulfides.

7. A process according to claim 1 in which the metal values include precious metals.

References Cited in the file of this patent UNITED STATES PATENTS 1,427,235 Sheridan Aug. 29, 1922 1,446,307 Hunt Feb. 20, 1923 1,672,924 Bacon June 12, 1928 2,007,176 Brinker July 9, 1935 2,429,477 Menefee et al. Oct. 21, 1947 2,537,842 McCauley et al. Jan. 9, 1951 2,697,034 Hadsel Dec. 14, 1954 FOREIGN PATENTS 528,500 Germany June 29, 1931 OTHER REFERENCES Morgan: American Gas Practice (1931), vol. 1, pages 806, 807.

Gandin: Floatation published by McGraw-Hill Book (30., N. Y., 1932, 1st ed., pages 344-346. 

1. A METHOD OF TREATING A MIXTRUE COMPRISING SULFUR IN ASSOCIATION WITH METAL VALUES TO OBTAIN A CONCENTRATE OF METAL VALUES IN PROCESS WHEREIN AN AQUEOUS SLURRY OF SAID MIXTURE IS HEATED TO AN ELEVATED TEMPERATURE ABOVE THE MELTING POINT OF SULFUR TO AGGLOMERATE THE SULFUR AND SAID SLURRY IS COOLED TO SOLIDIFY THE SULFUR AS PELLETS, WHICH COMPRISES: SUBJECTING SAID SLURRY TO SAID ELEVATED TEMPERATURE UNDER CONDITIONS OF TIME AND AGITATION FO FORM LIQUID SULFUR DROPLETS HAVING THEREWITH AN OPTION ASSOCCIATION OF SID METAL VALUES; COOLING TREATED SLURRY AND SEPARATING A SINGLE SOLID PHASE IN THE FORM OF PELLETS COMPRISING SULFUR AND METAL VALUES; DISPERSING SAID PELLETS IN AN AQUEOUS MEDIUM TO FORM A SLURRY; FURNISHING IN SAID SLURRY A MATERIAL WHICH IS CAPABLE OF DEPRESSING SULFIDE MINERALS IN THE FLOTATION OF OXIDIZED MINERALS; HEATING SAID SLURRY TO A TEMPERATURE ABOVE THE MELTING POINT OF SULFUR THEREIN; AGITATING SAID SLURRY AND MAINTAINING SAID TEMPERATURE FOR AT LEAST SUFFICIENT TIME TO SEPARATE SULFUR FROM THE METAL VALUES ASSOCIATED THEREWITH; COOLING SAID TREATED SLURRY TO OBTAIN SULFUR AND METAL VALUES AS SEPARATE SOLID PHASES; AND TREATING SAID COOLED SLURRY TO SEPARATE AND COLLECT A CONCENTRATE OF METAL VALUES. 